In recent years, thermally assisted (laser-assisted) magnetic recording has drawn an attention as a promising next generation high density magnetic recording technique. The technique is a technique for carrying out magnetic recording with respect to a high-coercivity magnetic recording medium, which is strong to heat fluctuation. Specifically, light is collected on a surface of such a magnetic recording medium so as to locally raise temperature of the magnetic recording medium. The temperature rise in such a portion of the magnetic recording medium causes reduction of the coercivity in the portion, with the result that the magnetic recording can be carried out with the use of a normal magnetic head.
Required for attainment of higher density thermally assisted magnetic field recording is size reduction of the collected light. Proposed in recent years is a technique using a near field which exceeds diffraction limit of light.
For example, Japanese Unexamined Patent Publication Tokukai 2001-319365 (published on Nov. 16, 2001; corresponding to US Patent Application 2001-0040868 A1) discloses a technique for using such a near field so as to attain the thermally assisted magnetic recording with respect to a magnetic recording film or an optical magnetic film. Specifically, such a thermally assisted magnetic recording using the near field is attained by forming a magnetic gap in the vicinity of an aperture in which the near field is generated. The formation of the magnetic gap is carried out by using a yoke extension section formed in a magnetic circuit constituting a thin film magnetic transducer.
That is, a flying recording head described in Japanese Unexamined Patent Publication Tokukai 2001-319365 includes a light shield body including an aperture having a size smaller than a size of laser light. The light shield body is provided in a position from which the laser light is irradiated, so that the laser light irradiated to the light shield body causes generation of the near field. Meanwhile, in the flying recording head, a magnetic field is generated by the thin film magnetic transducer, and the magnetic field thus generated is induced in the near field via the yoke extension section, with the result that the magnetic gap is formed. The magnetic gap is used for the recording onto the information recording medium, while raising the temperature of the information recording medium by using the near field.
Further, Japanese Unexamined Patent Publication Tokukai 2001-244564 (published on Sep. 7, 2001; corresponding to US Patent Application US2001-0021208 A1) and Japanese Unexamined Patent Publication Tokukai 2001-250251 (published on Sep. 14, 2001; corresponding to US Patent Application US2001-0021208 A1) do not describe a technique of generating the magnetic field, but describe a technique about a semiconductor laser including a part for generating the near field. See the description below.
Each of FIG. 74(a) and FIG. 74(b) illustrates an optical head, which is described in each of Japanese Unexamined Patent Publication Tokukai 2001-244564 (published on Sep. 7, 2001) and Japanese Unexamined Patent Publication Tokukai 2001-250251 (published on Sep. 14, 2001) and which includes such a semiconductor laser that has a metal light shield body having a fine aperture. As shown in FIG. 74(a), such an optical head 900 includes a flying slider 911. The flying slider 911 has a rear end portion 911a in which a semiconductor laser 920 is provided. The semiconductor laser 920 includes (i) a crystalline film 930, (ii) a high reflection multilayer film 910a provided in the rear end surface of the crystalline film 930, and (iii) a low reflection multilayer film 910b provided in the front end surface of the crystalline film 930. The high reflection multilayer film 910a has a reflectance different from that of the low reflection multilayer film 910b. The low reflection multilayer film 910b has a surface on which a metal light shield body 940 having a coaxial aperture 915 is provided. The coaxial aperture 915 is made up of (i) a rectangle-shaped minute aperture, and (ii) a rectangle-shaped center metal body which is provided such that the center of the center metal body coincides with the center of the minute aperture.
As such, the optical head 900 includes the semiconductor laser 920 having the metal light shielding member 940 in which the coaxial aperture 915 is formed. Such a single optical head 900 irradiates laser light from a laser oscillation region 980 to the coaxial aperture 915. This causes generation of a near field 960 in the vicinity of the minute aperture of the coaxial aperture 915. On this occasion, in cases where the optical head 900 is so positioned as to face a surface of a medium 970a provided on the substrate 970b as shown in FIG. 74(b), the optical head 900 irradiates laser from (i) the plan surface having the minute aperture in which the near field is generated, to (ii) the medium 970a. With this, the near field 960 can be irradiated to the surface (recording surface) of the medium 970a of the information recording medium 970, with the result that information can be recorded thereonto.
However, the conventional structures suffer from such a problem that good thermally assisted magnetic recording/reproduction cannot be carried out, at a high frequency, with respect to the minute region in the medium.
That is, in the structure of the flying recording head described in Japanese Unexamined Patent Publication Tokukai 2001-319365, the magnetic field is induced from the thin film magnetic transducer to the near field via the yoke extension section, so that the yoke extension section causes (i) strength attenuation of the magnetic field and (ii) propagation delay of thereof. The strength attenuation of the magnetic field gives rise to decrease of output for the writing, whereas the propagation delay thereof gives rise to slow responsiveness. For this reason, the flying recording head having such a structure is not suitable for the high frequency magnetic recording/reproduction.
On the other hand, in each structure of Japanese Unexamined Patent Publication Tokukai 2001-244564 and Japanese Unexamined Patent Publication Tokukai 2001-250251, when the near field generated in the minute aperture actually comes close to the surface of the medium, the near field resonates between (i) the plan surface in which the minute aperture is formed, and (ii) the surface of the medium; and the near field propagates within the plan surface. Accordingly, strength distribution of the near field varies in the minute aperture. For this reason, the techniques are not suitable for the near field assisted recording which requires the near field for the recording onto a minute region of the medium.
Note that, the wording “near field” in the present specification encompasses (i) a surface plasmon Dsp (surface-plasmon polariton), which is a surface electromagnetic wave generated on a surface of a material or generated in the vicinity of an interface of the material; (ii) a localized surface plasmon Dlsp (localized surface-plasmon polariton) which is locally excited in a solitary fine particle, a tip of a minute metal needle, etc.; and the like.